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View Full Version : Any 8080 programers out there?



Terry Yager
March 9th, 2004, 04:33 PM
I'm learning (teaching myself) to program the i8080, and have a question re: the F(lag) register. Does anyone know for certain what the designation of the flag bits are? I'm using several different sources to learn from, but there seems to be some confusion among the various authors. Some sources refer to the (S)ign flag, which is "set" (to a 1) if the number (in A) is + (positive) and "reset" (to zero) if the number is - (negative). Other sources refer to a M(inus) flag, which is set if the A-reg. contains a -(negative) number, the complete opposite as the "S" flag. DDT, the CP/M debugger calls it an "M" flag (when you dump the registers). At least one book I have uses both definitions in different parts of the book. (It was co-authored by two different people...hmmmmnnn...). I'm just getting more and more confused the more I read.

--T

P.S. I found a manual for Processor Technology's SOL debugger, which refers to a S(ign) flag. (The plot thickens...)

Terry Yager
March 9th, 2004, 11:06 PM
Found i8080 User Manual on-line. According to Intel, the (disputed) bit is a S(ign) bit. I guess they're the final authority, eh? (Now how am I ever gonna trust DDT again, if it's misleading me)?

--T

Terry Yager
March 9th, 2004, 11:38 PM
The S(ign) bit is SET (S=1) if the number is MINUS and RESET (S=0) if the number is PLUS! OK, fine...DDT didn't lie to me after all. (It tells me that the M(inus) flag is SET when the number is NEGATIVE). I think I got it now...

--T